Brake discs of the ventilated type are generally known, i.e. comprising a ventilated braking band which comprises two plates on which opposite braking surfaces are obtained suitable for acting in conjunction with opposite brake pads of a brake caliper which can be associated with the brake disc to exert the braking action, in which said two plates are spaced apart in axial direction, thus delimiting a gap.
Ventilated brake discs are provided with a plurality of axial connecting elements such as fins or pegs, which structurally connect said two plates to each other, thus forming said gap in conjunction with the two plates.
For example, this type of brake disc is known from International Patent Applications Nos. WO2011058594 and WO2012164465 of the same Applicant. Other examples are known from GB2286438 and GB2060796, GB2116654, DE102012024298, DE4332693, WO2008078352, EP2192321, DE202006017092, DE102004056645, DE19925003 and U.S. Pat. No. 5,526,905.
This type of brake disc has the advantage that the variously shaped connecting elements of the braking band delimit a plurality of ventilation channels in the gap between the plates, which are suitable for conveying a fluid current for cooling the brake disc when the brake disc rotates. The fins and pegs are alternated with protrusions mainly in order to provide improved cooling efficiency.
The need is strongly felt to cool the brake disc quickly and efficiently, and the contrasting need simultaneously is felt to lighten the brake disc, given that the disc is a non-suspended mass, as well as the contrasting need to maintain an adequate structural resistance which avoids the occurrence of fatigue cracks caused both by several thermal transients and by the braking actions.
In particular, it is important for the fluid current to be inside the gap during turbulent operation in order to maximize the cooling.
Moreover, in particular, temperatures of the brake disc which are too high cause a decreased efficiency of the braking action and simultaneously may cause the occurrence of thermal cracks in the body of the brake disc itself.
Solutions are known which have attempted to resolve these contrasting needs. For example, International Patent Application No. WO2015092671 of the same Applicant shows a ventilated brake disc comprising connecting elements between the two plates with which connecting protrusions or fitting burrs are associated, which extend from the connecting elements thus connecting them to the plates.
Other solutions are known from WO2008136032, DE102013210700, GB2282197, DE4332693, DE19925003, DE4040423, DE7603818U1, DE10157284 and DE2637493.
Although they are partly advantageous in reducing the occurrence of thermal cracks in the body of the brake disc, such solutions in any case have certain drawbacks.
Indeed, although the provision of said connecting burrs increases the turbulence of the cooling fluid current and the heat exchange surface of the connecting elements, it does not necessarily increase the volume, and therefore the weight, of the connecting elements themselves and of the whole brake disc. Accordingly, in order to ensure the structural integrity of the brake disc when it is in operating conditions, the above-mentioned increase in weight imposes making connecting elements, such as fins or pegs, having a particularly fat cross section, for example diamond-shaped, as is clearly apparent for example, from the fin cross-sections shown in FIGS. 2, 4, 5 and 6 of document No. WO2015092671. Additionally, as is known, the weight of the brake disc is directly proportional with the inertia of the brake disc during the braking.
The need is therefore strongly felt to obviate the drawbacks of the known art mentioned hereto.
Therefore, the need is felt to provide a structurally resistant ventilated brake disc while allowing the possibility of making lightweight and thin connecting elements, thus simultaneously facilitating the heat exchange and the formation of turbulent flows.